The manufacture and use of man-made fibers for use in woven and nonwoven textiles and in absorbent webs in disposable products, e.g., diapers, catamenials, etc., has been known for some time. Good absorbency and wicking properties are generally desirable attributes in such products. In absorbent webs, the desirability for high absorbency and wicking performance is apparent in that it is the primary purpose of such webs to absorb deposited fluids. It is often equally essential that the webs have the capacity to wick the fluids away from the region of deposit in order to prevent failure at such deposit region, and in order to more fully utilize the absorbent capacity of the web. In textile materials, worn as clothing, it is often desirable to wick perspiration away from the skin in order to facilitate evaporation of the perspiration and to prevent a "clammy" sensation of the skin.
Conventionally, absorbent webs have been made from natural cellulosic fibers. Absorbency in such webs was achieved by a combination of fluid penetration into the interior of the cellulosic fiber lumen and retention in interfiber capillary spaces. Wicking was primarily achieved through the action of such interfiber capillary spaces. More recently, many absorbent webs for disposable absorbent products, especially diapers, have been supplemented with polymeric gelling agents which absorb fluids to form an insoluble gel. The use of such polymeric gelling agents has facilitated the design of thin, low bulk diapers. However, the usage of such polymeric gelling agents has also increased the importance of the wicking performance of the fibers since a significant portion of the absorbency function of the fibers is performed by the polymeric gelling agents. However, due to limitations of fluid distribution properties of fibrous webs conventionally used to acquire and distribute discharged body fluids, substantial portions of the fibers, the polymeric gelling material, or other absorbent materials, are often not efficiently utilized. In particular, large areas of the web that are not proximate to the region of fluid discharge remain often unused, or not efficiently utilized, even when other regions of the web proximate to the region of fluid discharge may become oversaturated to the point of failure (i.e., leakage). Thus, it is highly desirable to provide fibrous materials that provide improved wicking performance relative to conventionally used fibers and webs, that are additionally economically viable, and that can efficiently transport fluid in a low bulk absorbent article design.
A significant drawback of conventional fibers is that their ability to wick fluids is highly dependent upon the bulk density of the web into which they are formed. In addition to the established trade-offs relating to interfiber capillary size, wicking rate, and volumetric flow rate, another factor which must be considered when choosing design parameters is tactile softness of the web being formed. In general, softness will decrease as bulk density and interfiber capillarity are increased. Thus, aesthetic and structural design considerations must often be compromised to attain desired absorbency and wicking performance in the design of absorbent products. These same considerations and drawbacks are additionally applicable to webs made of conventional synthetic fibers, such as nylon, polyester, polypropylene, and chemical cellulose-based fibers.
One technique that has been used to increase wicking performance of fibrous webs is to hydrophilize the fibers. Although such treatments are effective for increasing wicking ability, they do not increase fluid distribution properties of the fibers such that significantly larger amounts of fluid can be efficiently transported to regions of absorbent articles distant from the region of fluid discharge. Hydrophilization treatments additionally do not affect the trade-offs conventionally experienced regarding poor capillarity for soft, low density webs.
Another approach that has been investigated is to form fibers having intrafiber capillary channels. These fibers have the ability to wick fluids individually, without necessarily relying upon the close proximity of adjacent fibers to form interfiber capillary pathways. A variety of fibers with grooves or intra-fiber channels have been proposed. Though by no means intended to represent a comprehensive review of the art, it is believed that the following references at least are indicative of the published art.
French Patent 955,625, Paul Chevalier, "Improvements in Spinning Artificial Fiber", published Jan. 16, 1950, discloses fibers of synthetic origin with allegedly improved capillarity. The fibers are said to have continuous or discontinuous grooves positioned in the longitudinal direction, i.e., parallel to the fiber axis. The fibers may have a central nucleus from which radiate radial leaves. This patent also discloses a process for making the fibers involving a first spinneret for forming the fibers into the desired shape and a second spinneret in direct communication with the first, separated from the first by an insulating plate, for cooling the fiber. The second spinneret is in contact with a cooling element.
U.S. Pat. No. 3,121,040, Gilbert Shaw, "Unoriented Polyolefin Filaments", issued Feb. 11, 1964, discloses a variety of plastic filaments, and a process for making them, which assertedly exhibit good recovery after deformation and resisting orientation (i.e., matting) upon use in such applications as paint brushes. These objects are said to be achieved by preparing fibers having cross-sections consisting of interconnected webs with web length, web thickness, and radius of particular, specified requirements.
U.S. Pat. No. 4,054,709, M. N. Belitsin, et al., "Man-Made Fibre, Yarn and Textile Produced Therefrom", issued Oct. 18, 1977, discloses fibers of polycaproamide and polyethylene terephthalate displaying a cross sectional shape formed of at least two elements formed of intersecting rays which define open capillary channels and a bridge interconnecting particular rays of the elements. The rays intersect at angles of from 10.degree. to 70.degree. to form the capillary channels. The fibers are said to exhibit an appearance and moisture conductivity and absorption approaching natural silk.
U.S. Pat. No. 4,381,325, Utaka Masuda, et al., "Liquid Retaining Synthetic Fiber, Process for Producing the Same, and Products", issued Apr. 26, 1983 discloses a liquid-retaining synthetic fiber having a substantially pointed free end and a tapered portion. The fibers disclosed include embodiments having a plurality of channels running along the axial length of the fibers.
European Patent Application 883 069 87.4, publication number 0,301,874, published Feb. 1, 1989, Andrew G. Wilkes and Alan J. Bartholomew, "Cellulosic Fibre", discloses viscose filaments having multi-limbed cross-section, e.g., Y-, X-, H-, and T- shapes which are said to be useful for absorbent products and woven and nonwoven fabrics.
U.S. Pat. No. 4,286,005, Richard M. Berger, "Ink Reservoir Element for Use in a Marking Instrument, and Method and Apparatus for Producing Same", issued Aug. 25, 1981, discloses an ink reservoir element formed from a coherent sheet of flexible thermoplastic fibrous material or form-attenuated extruded polyester fabric, which has been uniformly embossed with a series of parallel grooves. The embossed sheet is compacted and bonded into a dimensionally stable body whose longitudinal axis extends parallel to the embossed grooves.
U.S. Pat. No. 4,623,329, James L. Drobish, et al., "Drainage and Infusion Catheters Having a Capillary Sleeve Forming a Reservoir for a Fluid Antimicrobial Agent", issued Nov. 18, 1986, discloses catheter tubs provided at the inner surfaces with longitudinally extending capillary channels or grooves. The grooves preferably exhibit a favorable surface contact angle for the particular fluid to be dispensed. Surface treatments to alter the surface contact angle can be applied.
Japanese Patent Application 151617-1979, published Nov. 29, 1979, Teijin KK, "Synthetic Fibers", discloses various modified-profile synthetic fibers, especially of polyester or polyamide, having a cross-section shape characterized by fine pores running in the axial direction having diameter of 0.01 microns to 5 microns and a total cross-sectional area of the pores of 0.016 to 50% of the total cross-sectional area of the fibers. The fibers can have additives for increasing water absorption properties.
European Patent Application EP-A-391814, published Oct. 10, 1990, Eastman Kodak Company, "Fibers Capable of Spontaneously Transporting Fluids," discloses fibers which are said to be especially effective at transporting fluids such as water on their surfaces. Such fibers are defined by a mathematical relationship between the contact angle of fluid to be transported by the fibers and a "shape factor" which is determined by the geometric configuration of a cross-section of the fiber.
In spite of these advances, it remains desirable to provide flexible, collapse-resistant, capillary channel structures that exhibit further improved intrafiber absorbent capacity and wicking ability. It is an object of this invention to provide such structures which additionally can be produced and utilized with improved economics relative to those previously shown in the arts. More specifically, it is an object of this invention to provide such structures which exhibit improved absorptive capacity on a unit weight basis in combination with high capillary suction (i.e., high height of rise of fluid against gravity) which also resist collapse of the capillary channels during handling and use.
It is another object of this invention to provide structures as described immediately above which are in the form of fibers, and which can be used for woven and nonwoven textile materials or in the form of webs or bundles, such as in absorbent articles (e.g., diapers, catamenials, etc.).
It is yet another object of this invention to provide such capillary channel structures in the form of a flexible sheet or film.
It is still another object to provide absorbent articles, including disposable absorbent articles, incorporating such capillary channel fibers as an element thereof.
It is another object of this invention to provide flexible, collapse-resistant capillary channel structures which are especially suited for transporting and/or storing aqueous fluids.
It is still another object to provide flexible, collapse-resistant capillary channel structures which are especially suited for transported and/or storing organic fluids, e.g., oil.
It is yet another object to provide a process for making improved capillary channel structures which can meet the above objects.
It is yet a further object to provide equipment which facilitates the manufacture of such improved capillary channel structures which can be utilized in conjunction with the above-reference process.
These objects and still other benefits and uses of the present invention can be attained in the manner described hereafter.